Creating Mailbox Plans and Global Mailbox Plans

Mailbox plan is a similar to hosting plan. It's a set of quotas, but only for Hosted Exchange. Mailbox plan is used as a template for creating customer mailboxes. You can create mailbox using some mailbox plan and then apply other mailbox plan with other quotas in future, for example if it needs to be changed from 10GB limit to 20GB.

Note: your mailbox plan should have same or less quotas as your hosting plan. For example, if hosting plan allows you to have 10 maximum recipients, but you choose more than 10 in mailbox plan, then mailbox creation based on this plan will fail due to exceeded quota.